The call of the last week has been ryegrass and/or Poa escaping burndown in a number of fields that have been or will be planted to corn. In most cases the ryegrass escaped a glyphosate plus dicamba burndown.
The reason for the lack of control is the continued evolution of glyphosate-resistance in both ryegrass and Poa populations as well as dicamba decreasing the effectiveness of glyphosate on those two winter annual grass species.
The question on how to control ryegrass in a standing corn crop really has no “sure fire” answer. One good option is Steadfast Q which can be effective on ryegrass even at cooler temperatures. The catch is that some ryegrass in the state is ALS-resistant so Steadfast Q will not be effective in those cases. Another effective option, if the corn hybrid is Liberty Link, is to apply a 32 oz/A of Liberty.
Tankmixing in a quart of atrazine with the Liberty can improve the control. Please keep in mind when utilizing Liberty in corn applications in April or early May is that air temperatures can be too cool for Liberty to be effective. In order to get the best ryegrass control with Liberty, try to pick a warm spell where temperatures are in the mid-80s and apply it during the middle of the day.
With respect to Poa, our research has indicated that Gramoxone or Reviton + glyphosate provides good control. They typically are not as consistent on ryegrass as the options mentioned earlier. Of course neither Gramoxone nor Reviton can be applied POST in corn. If Poa is present and the corn has emerged then the typical premixes commonly used in Tennessee like Capreno, Halex GT or Acuron GT can all be effective on Poa if they are tankmixed with 48 ozs/A of atrazine.